An image forming apparatus uses developer to form an image onto a recording medium. There has been proposed a conventional image forming apparatus that detects a residual amount of developer. A linear function is derived based on both of: a predetermined initial filling amount of the developer, whose data is previously stored in the image forming apparatus as reference use information; and a residual amount of the developer that actually remains after a lapse of a prescribed number of days. Based on the linear function, a specific date on which printing is estimated to become impossible is computed.